The present invention relates to an improved cracking catalyst, a process for forming the catalyst, and to a cracking process.
In the catalytic cracking of hydrocarbons, contaminants, such as nickel, vanadium, iron, and copper become deposited on the cracking catalyst from the feedstock impairing its ability to convert the feedstock to gasoline and enhancing its activity for converting the feedstock to coke and hydrogen, which are generally considered to be less desirable products than gasoline. It has been disclosed, by Cimbalo et al., "Oil & Gas Journal," Vol. 70, No. 20, May, 1972, pages 112, 114, 118, 120, and 122, for example, that the ratio between the molecular hydrogen and methane in the gaseous product from a catalytic cracking unit is representative of the intrinsic activity of the catalyst for converting the feedstock to coke and hydrogen and is relatively independent of commonly altered process variables such as conversion. Generally speaking, then, it is extremely desirable to provide cracking processes characterized by a low molecular hydrogen to methane ratio in the cracked product. The circulation of a passivating agent, such as antimony compounds in the catalytic cracking unit together with the catalyst lowers the hydrogen-to-methane mol ratio and yields greater gasoline production where contaminants are on the catalyst, for example.
In certain types of catalytic cracking units, especially those which employ a relatively large catalyst particle, for example, Thermofor (TCC) or Houdriflow units, in which the catalyst particles are beads commonly within the size range from about 500 to about 10,000 microns in size, catalyst attrition and erosion of the cracking unit by the catalyst are serious problems. A typical bead catalyst is a right cylinder of about 5 mm diameter by 5 mm length. The catalyst attrites to fines, which can escape the unit in the regenerator off-gases as a dust and perhaps cause environmental problems as well as an economic burden in replacing the amount of catalyst lost, which can range up to several thousands of dollars per day. It is known that stack opacity, that is, an inverse measurement of the clarity of the regnerator off-gases, is representative of the amount of catalyst fines being produced by and lost from the cracking unit. Generally speaking, then, it is desirable to provide cracking processes characterized by low stack opacity. It has been disclosed in U.S. Pat. No 3,030,300, for example, that the circulation of a glazing agent, such as strontium oxide, in a catalytic cracking unit together with the cracking catalyst will lower stack opacity and cause a reduction in unit erosion and catalyst losses from the unit, although barium sulfate is the glazing agent which has gained commercial acceptance.